1. Field of the Invention
The present invention relates to a unit to separate gas from a liquid stream and, more particularly, to such a unit for separating gas from an oil and water production stream, as well as desurging the flow of such production stream.
2. Setting of the Invention
In the production of oil from subterranean reservoirs, the production stream, can contain, in addition to oil, water and entrained gas, such as methane, butane and the like. Before the oil can be transported or introduced into a pipeline, the water and the gas need to be removed. Oil-water separators and degassers are well known; however, in certain situations these oil-water separators and degassers do not perform adequately. Further, the oil-water separators and degassers are usually equipped with mechanical flow control devices, such as float level controllers and dump valves, which require periodic maintenance and tend to be expensive.
One such special situation where conventional oil-water separators and degassers are inadequate is when these devices are used in conjunction with a vortex separation tank. A vortex separation tank is a large hollow tank into which is tangentially introduced the production stream. The oil and water separate by their density differences as the oil slowly spirals around the internal walls of the tank. It has been found that when an oil-water production stream is introduced into such a vortex separation tank, any entrained gas will bubble through the oil and water which agitates the fluid thus reducing the overall separation effectiveness of the separation process. Also, when the production stream is introduced into the vortex separation tank the gas begins to separate and form large bubbles within the production stream piping which then enhance or cause fluid surges, which drastically reduce the separation effectiveness of the separation process in a vortex separator tank. Flume-type and conventional degassers have been tried with vortex separation tanks to prevent such surges; however, these degassers are expensive, have mechanical control devices which require maintenance, and do not effectively prevent or eliminate production stream surges caused by pulses in flow rates. There exists a need for a simple, essentially maintenance free device to degas an oil and water production stream and to also desurge the flow of the production stream.